(1) Field of the Invention
The present invention relates to a valve body for use in a cap with a valve, such as a fuel cap or a radiator cap for an automobile.
(2) Description of the Prior Art
A valve body for use in a fuel cap of the type shown in FIGS. 1 to 2 is known (see Japanese Patent Laid-Open No. 116974/1985).
The valve body 7, of FIGS. 1 and 2 made from a rubbery elastic material, such as rubber or thermoplastic elastmer, has a disk-like form. The valve body 7 comprises a securing portion 7a, at the central portion thereof, having a downward-projection 7b whose tip portion expands so as to fit into a securing hole 6a disposed in a valve support plate 6. The valve body 7 further comprises an arm portion 7c which extends outwardly in the radial direction such as to be parallel to the valve body support plate 6 starting from the securing portion 7a, and a lip portion 7d which is disposed at the outer periphery of the arm portion 7c around the entire circumference of the same in such a manner that it projects upward.
The lip portion 7d seals the lower surface of a ceiling portion 2a in such a manner that it seals the area around a flow passage aperture 2b which is bored through the center of the ceiling portion 2a of a main cap body 2, which portion opposes the valve body support plate 6. The lip portion 7d is caused to abut against the circumferential portion of the flow passage aperture 2b by the spring force of a coil spring 5. A lower end portion of the coil spring 5 is held by a spring support plate 4 which is secured, in an undercutting manner, at a lower portion of the inner surface of the main cap body 2. On the other hand, the top end portion of the coil spring 5 is positioned in contact with the lower surface of the valve body support plate 6 so as to give an upward bias to the support plate 6 with the valve body 7.
An annular groove 7e is formed between the securing portion 7a and the outer edge portion of the reverse side of the arm portion 7c around the entire circumference thereof. This annular groove 7e is adapted to form a prescribed gap h between the reverse side of the arm portion 7c and the valve support plate 6 when the lip portion 7d does not abut against the circumferential portion of the fluid passage aperture 2b. This annular groove 7e is so designed that it corresponds to the profile irregularities (in particular, surface smoothness) of the lower circumferential portion of the flow passage aperture 2b of the ceiling portion 2a, the valve body support plate 6, and the lip portion 7d. That is, this annular groove 7e is arranged to absorb any error in surface smoothness existing in any of these portions by being readily deflected in the axial direction of the valve body 7 relative to the supporting point, that is, the portion connecting the arm portion 7c and the securing portion 7a.
Reference numeral 3 represents a top cover which is installed on the top of the main cap body 2. Reference numeral 10 represents a filler neck of a fuel chamber.
The operation of the fuel cap 1 will now be described.
When the pressure inside the fuel chamber drops below a predetermined negative pressure, the valve body 7 with the valve body support plate 6 is lowered against the spring force of the coil spring 5. The lip portion 7d is separated from the lower surface of the ceiling portion 2a around the flow passage aperture 2b in the ceiling portion 2a of the main cap body 2. The separation causes the flow passage aperture 2b to open, whereby air is introduced through the flow passage aperture 2b into the fuel chamber, and the negative pressure state of the fuel chamber inside can thus be restored.
In the conventional valve body 7, the annular groove 7e is formed on the reverse side of the arm portion 7c, starting from the securing portion 7a to the edge of the arm portion 7c, completely around the arm portion 7c. A predetermined gap h is, therefore, formed between the reverse side of the arm portion 7c and the valve body support plate 6, when the lip portion 7d does not abut against the ceiling portion 2a. Therefore, in this valve body 7, the lip portion 7d is capable of being easily deflected in the axial direction of the valve body 7 relative to a supporting point: the portion connecting the arm portion 7c and the securing portion 7a. The deflection of the lip portion 7d is capable of absorbing any errors occuring on the lower surface of the ceiling portion 2a of the main cap body 2 in the circumferential portion of the flow passage aperture 2b, the valve body support plate 6, and the lip portion 7d, even if the accuracy in surface smoothness is insufficient.
In a case where the valve body 7 is operated at a low pressure using a coil spring 5 with a low spring constant, it is not sufficient to absorb the aforementioned errors solely by the provision of a predetermined gap on the reverse side of the arm portion 7c. A precise control of the accuracy of surface smoothness of the lip portion 7d, and its sealing portion, that is, the ceiling portion 2a of the main cap body is necessary.
In the conventional valve body 7, the annular lip portion 7d is projected around the entire outer circumference of the top surface thereof The thickness of the portion at which the lip portion 7d is formed is, of course, greater than that of the portion adjacent to and continued from the lip portion 7d.
A rubbery elastic material flows in a mold cavity from the securing portion 7a toward the lip portion 7d in the case, for example, where a gate is provided beneath the projection 7b at the center of the valve body 7 when the latter is formed. Therefore, if the thickness of the lip portion 7d is great, the pressure available for pressing the rubbery elastic material rapidly decreases in the lip portion 7d. There is a risk that undesired air pockets may be formed in the lip portion 7d. If such air pockets are generated, it is impossible for a top portion 7t of the lip portion 7d, which top portion abuts against the portion to be sealed, to keep the profile irregularity (smoothness: substantially .+-.5 .mu.m) which is necessary from the viewpoint of sensitivity in opening the valve and retention of sealing capability. Valves which include such air pockets form defective products.